U.S. patent application number 12/979967 was filed with the patent office on 2012-01-05 for knuckle formed through the use of improved external and internal sand cores and method of manufacture.
Invention is credited to F. Andrew Nibouar, Jerry R. Smerecky, Douglas Smith.
Application Number | 20120000877 12/979967 |
Document ID | / |
Family ID | 43806786 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120000877 |
Kind Code |
A1 |
Smith; Douglas ; et
al. |
January 5, 2012 |
Knuckle Formed Through The Use Of Improved External and Internal
Sand Cores and Method of Manufacture
Abstract
A method for manufacturing a railcar coupler knuckle, said
method includes providing a cope mold portion and a drag mold
portion. The cope and drag mold portions have internal walls that
define at least in part perimeter boundaries of a coupler knuckle
mold cavity. At least one chill core is positioned within one of
the cope mold portion and the drag mold portion. The cope and drag
mold portions are closed, with the at least one core therebetween,
and the closed cope and drag mold portions and the chill core
define a parting line. The mold cavity is filled with a molten
metal, which solidifies after filling to form a casting. The
casting includes a pulling face portion defined by the chill core,
and a central section of the pulling face portion does not contain
the parting line and requires no finish grinding upon its
formation.
Inventors: |
Smith; Douglas; (Eldridge,
IA) ; Nibouar; F. Andrew; (Chicago, IL) ;
Smerecky; Jerry R.; (Roselle, IL) |
Family ID: |
43806786 |
Appl. No.: |
12/979967 |
Filed: |
December 28, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61291584 |
Dec 31, 2009 |
|
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|
Current U.S.
Class: |
213/155 ;
164/137; 213/75R |
Current CPC
Class: |
B22C 9/108 20130101;
B22D 15/00 20130101; B61G 3/04 20130101; B22C 9/02 20130101 |
Class at
Publication: |
213/155 ;
164/137; 213/75.R |
International
Class: |
B61G 7/00 20060101
B61G007/00; B22D 25/02 20060101 B22D025/02 |
Claims
1. A method for manufacturing a railcar coupler knuckle, said
method comprising: providing a cope mold portion and a drag mold
portion, the cope and drag mold portions having internal walls
defining at least in part perimeter boundaries of a coupler knuckle
mold cavity; positioning at least one chill core within one of the
cope mold portion and the drag mold portion; closing the cope and
drag mold portions with the at least one core therebetween, the
closed cope and drag mold portions and the chill core defining a
parting line; filling the mold cavity with a molten metal, the
molten metal solidifying after filling to form a casting including
a pulling face portion defined by the chill core, wherein a central
section of the pulling face portion does not contain the parting
line and requires no finish grinding upon its formation; and
reducing micro-shrinkage in a high-stressed area of the
casting.
2. The method of claim 1, wherein at least a portion of the chill
core further comprises a high-density casting sand.
3. The method of claim 2, wherein the high-density casting sand
includes chromite.
4. The method of claim 2, wherein the high-density casting sand
includes zircon.
5. The method of claim 1, wherein the chill core is formed from
graphite.
6. The method of claim 1, wherein the chill core is metallic.
7. The method of claim 6, wherein the chill core formed from cast
gray iron.
8. The method of claim 1, wherein the coupler knuckle mold cavity
defines a finger section that with the external core defines the
pulling face portion.
9. The method of claim 1, further comprising positioning at least
one internal core formed at least in part from a high-density
casting sand within one of the cope mold and drag mold
portions.
10. The method of claim 1, further comprising forming at least
portions of the parting line at upper and lower portions of the
pulling face portion.
11. The method of claim 1, further comprising forming the central
portion of the pulling face portion to be substantially flat.
12. A railcar coupler assembly, comprising: a casting having a
bearing surface formed at least in part by an external core
positioned within a mold; a parting line formed on at least a
portion of the casting that is formed by the external core and the
mold but is not formed on the bearing surface; wherein the bearing
surface requires no grinding upon its formation and wherein the
external core reduces micro-shrinkage in the area of the bearing
surface.
13. The railcar coupler assembly of claim 12, wherein the casting
is a coupler knuckle, and wherein the bearing surface comprises at
least a portion of a pulling face portion.
14. The railcar coupler assembly of claim 13, wherein portions of
the parting line are located at upper and lower portions of the
knuckle.
15. The railcar coupler assembly of claim 12, further comprising at
least one internal core disposed within the mold to define an
internal cavity of the casting, and wherein the internal core is
made from a high-density casting sand such that the portion of the
casting defined by the internal core made from a high-density
casting sand requires no grinding upon the casting's formation.
16. The railcar coupler assembly of claim 12 further comprising at
least one internal core disposed within the mold to define an
internal cavity of the casting, wherein the internal and external
cores are formed from chromite and reduce micro-shrinkage in a high
stressed area of the bearing surface.
17. The railcar coupler assembly of claim 12, wherein the casting
is a coupler body.
18. The railcar coupler assembly of claim 12, wherein at least a
portion of the external core further comprises a high-density
casting sand.
19. The railcar coupler assembly of claim 18, wherein the
high-density casting sand includes chromite.
20. The railcar coupler assembly of claim 18, wherein the
high-density casting sand includes zircon.
21. The railcar coupler assembly of claim 12, wherein the external
core is formed from graphite.
22. The railcar coupler assembly of claim 12, wherein the external
core is metallic.
23. The railcar coupler assembly of claim 22, wherein the external
core is formed from cast gray iron.
24. The railcar coupler assembly of claim 12, wherein portions of
the parting line correspond to outer portions of the external
core.
25. A railcar coupler knuckle, comprising: a casting having a
pulling face portion; the pulling face portion defining a contour
of the knuckle for interfacing with another coupler knuckle;
wherein a pulling face portion of the casting is defined at least
in part by an external core disposed within a mold, and wherein the
external core includes a chill core portion that defines a central
portion of the pulling face portion such that the central portion
of the pulling face portion does not include a parting line and
requires no grinding upon its formation.
26. The coupler knuckle of claim 25, wherein at least the chill
core portion of the external core further comprises a high-density
casting sand.
27. The coupler knuckle of claim 26, wherein the high-density
casting sand includes chromite.
28. The coupler knuckle of claim 26, wherein the high-density
casting sand includes zircon.
29. The coupler knuckle of claim 25, wherein the external core is
made from graphite.
30. The coupler knuckle of claim 25, wherein the external core is
metallic.
31. The coupler knuckle of claim 30, wherein the external core is
made from cast gray iron.
32. The coupler knuckle of claim 25, further comprising at least
one internal core to define a cavity of the casting, and wherein at
least a portion of the internal core includes a chill core
portion.
33. The coupler knuckle of claim 32, wherein the chill core
portions of the internal and external cores are formed from
chromite and reduce micro-shrinkage in a high stressed area of the
pulling face portion.
34. The coupler knuckle of claim 25, wherein portions of the
parting line are located at upper and lower portions of the pulling
face portion.
Description
RELATED APPLICATIONS
[0001] The present patent document claims the benefit of the filing
date under 35 U.S.C. .sctn.119(e) of Provisional U.S. Patent
Application Ser. No. 61/291,584, filed Dec. 31, 2009, which is
hereby incorporated by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present embodiments relate generally to the field of
railroad couplers, and more specifically, to the manufacture of an
improved knuckle through the use of an improved sand core.
[0004] 2. Related Art
[0005] Railcar couplers are disposed at each end of a railway car
to enable joining one end of such railway car to an adjacently
disposed end of another railway car. The engageable portion of each
of these couplers is known in the railway art as a knuckle.
[0006] Typically, a knuckle is manufactured by a mold and several
cores that are disposed within the mold. The mold shapes the
outside of a casting. The cores are disposed to shape the inside or
outside of a casting. Without the inside cores, the casting would
be made of solid metal. The outside cores help shape the exterior
of the casting. The inside cores commonly are referred to as a
finger core in the front portion of the knuckle, a pivot pin core
in the center of the knuckle, and a kidney core at the rear of a
knuckle, and form the cavities in the knuckle upon casting.
[0007] During the casting process itself, the interrelationship of
the mold and three cores (sometimes manufactured as one or two
piece cores) disposed within the mold are critical to producing a
satisfactory railway coupler knuckle. Many knuckles fail from
internal and/or external inconsistencies in the metal throughout
the thickness of the knuckle. If one or more cores move during the
casting process, then some knuckle walls may end up thinner than
others, resulting in offset loading and, in turn, resulting in an
increased failure risk during use of the knuckle.
[0008] The external features of a coupler knuckle should meet
railroad industry standards both because of initial acceptance of
the knuckle and for its successful performance in service. One
external feature that must be formed properly for successful
knuckle performance in service is the pulling face contour. The
pulling faces of mating couplers contact each other when freight
cars are coupled together and transmit the forces pulling the
train. The pulling forces within a train can be substantial. For
this reason, railroad industry standards exist that specify the
shape of the pulling face contour. Inconsistent or out of tolerance
pulling face contours can result in poor coupling/uncoupling
performance of the coupler or in detrimental load paths for the
pulling load. One patent that discusses the importance of the
proper performance of the pulling face is U.S. Pat. No. 7,337,826
entitled "Railway Car Coupler Knuckle Having Improved Bearing
Surface." The '826 patent describes techniques for casting a
knuckle coupler with an enhanced bearing surface. The '826 patent,
however, is silent regarding as to addressing the imperfections
that can form on the knuckle during casting.
[0009] Coupler knuckles are generally manufactured from cast steel
or alloys. Typically, silica sand or silica sand derivatives known
in the art are used to create the mold walls and the cores. Such
sands, however, have several potential drawbacks, which can
adversely affect the knuckle's surface finish or its ability to
maintain required dimensional control, which in turn can lead to
the premature failure of the knuckle and increase maintenance costs
as a result of premature failure.
[0010] By way of example, when a molten metal is introduced into a
mold during casting, it is prone to shrinking as it cools and
solidifies. This is known as "shrinkage" or "micro-shrinkage" and
occurs because most metals are less dense as a liquid than as a
solid. Shrinkage may occur on the outside of the casting, the
inside of the casting, or both. Shrinkage may lead to the knuckle
to form shrinkage defects and even a void in certain portions of
the knuckle. This could cause the coupler to prematurely wear or
result in premature fatigue and/or failure.
[0011] One technique used to overcome micro-shrinkage is the
inclusion of risers in the mold to feed the volumes of the casting
that are prone to shrinkage with additional casting material as it
cools. However, once the knuckle is cast, the risers must be
removed, typically by surface grinding. This may cause damage to
the knuckle's surface and cause the knuckle to prematurely fatigue
and/or fail. Moreover, risers and/or large ingates, i.e., material
that connects the risers to the casting, are limited in their
ability to provide for a uniform thickness throughout the casting,
maintain precise part profile, and lose their effectiveness in
areas further away from the riser.
[0012] Another technique used to address micro-shrinkage issues is
the addition of metal chills. These may be external chills, which
may be placed along the mold walls at predetermined locations, or
may be internal chills. Internal chills can be pieces of metal that
are strategically placed inside the mold cavity and ultimately
become part of the casting. Chills absorb and remove the heat from
the poured metal in the location of the chill in order to promote
solidification and limit the amount of shrinkage in the vicinity of
the small area in which they are located. External chills, however,
may leave scars or other defects on a casting's surface that
requires the casting to undergo extra finishing operations such as
grinding, which may adversely affect the knuckle's surface finish.
External chills add additional cost, and due to their manual
application can result in inconsistent quality. Sometimes personnel
inadvertently neglect the installations of chills or place them in
the incorrect location. Internal chills add cost because they must
be made of the same material, or at least compatible, with the
casting. Moreover, chills may not fuse properly with the casting,
thus causing premature failure or again requiring the casting to
undergo a further finishing and/or repair process. Moreover, chills
must be clean and free of rust or other impurities so as not to
inhibit the solidification process.
[0013] Another drawback associated with silica sand and its
derivatives is their higher rate of thermal expansion during the
casting process. This may cause the mold to develop buckles and
ultimately crack, such that the molten metal will enter the crack
and create a fin projecting from the casting surface (also known as
a "vein"). It is preferred that these veins are removed, again
typically through a grinding process, which again may result in
fatigue failures, and correspondingly increases the finishing
cost.
SUMMARY OF INVENTION
[0014] In a first embodiment, a method for manufacturing a railcar
coupler knuckle includes providing a cope mold portion and a drag
mold portion. The cope and drag mold portions have internal walls
defining at least in part perimeter boundaries of a coupler knuckle
mold cavity. At least one chill core is positioned within one of
the cope mold portion and the drag mold portion. The cope and drag
mold portions are closed with the chill core there between, and the
closed cope and draft mold portions and the chill core define a
parting line. The mold cavity is filled with a molten metal and
solidifies to form a casting that includes a pulling face portion
defined by the chill core. A central section of the pulling face
portion does not contain the parting line and requires no finish
grinding.
[0015] A railcar coupler assembly also is provided that includes a
casting having a bearing surface formed at least in part by an
external core positioned within a mold. A parting line is formed on
at least a portion of the casting that is formed by the external
core and the mold but is not formed on the bearing surface. The
bearing surface requires no grinding upon its formation and the
external core reduces micro-shrinkage in the area of the bearing
surface.
[0016] A railcar coupler knuckle also is provided that has a
pulling face portion. The pulling face portion defines a contour of
the knuckle for interfacing with another coupler knuckle. A pulling
face portion of the casting is defined at least in part by an
external core disposed within a mold. The external core includes a
chill core portion that defines a central portion of the pulling
face portion such that the central portion does not include a
parting line and requires no grinding upon its formation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The system may be better understood with reference to the
following drawings and description. The components in the figures
are not necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention. Moreover, in the
figures, like-referenced numerals designate corresponding parts
throughout the different views.
[0018] FIG. 1 is a view of cope and drag portions of a mold to cast
a coupler knuckle, with internal and external cores disposed within
the cavity of the drag mold portion.
[0019] FIG. 2 is a top perspective view of the drag mold portion of
FIG. 1, with internal and external cores disposed within the
cavity.
[0020] FIG. 3 is a side view of the drag mold portion of FIG. 2
showing the cope mold portion being lowered over the drag mold
portion and the internal and external cores.
[0021] FIG. 4 is a side view of a finger core and a combined kidney
and pivot pin core.
[0022] FIG. 5 is a top view of a cast coupler knuckle.
[0023] FIG. 5A is the cross-section view along line A-A of the
coupler knuckle of FIG. 5.
[0024] FIG. 5B is the cross-section view along line B-B of the
coupler knuckle of FIG. 5.
[0025] FIG. 6 is a perspective view of a cast coupler knuckle.
[0026] FIG. 7 shows a pair of coupler knuckles in engagement.
[0027] FIG. 8 shows a cope mold portion lowered onto a drag mold
portion.
[0028] FIG. 9 shows a coupler knuckle in combination with a
coupler.
DETAILED DESCRIPTION
[0029] In some cases, well known structures, materials, or
operations are not shown or described in detail. Furthermore, the
described features, structures, or characteristics may be combined
in any suitable manner in one or more embodiments. It will also be
readily understood that the components of the embodiments as
generally described and illustrated in the Figures herein could be
arranged and designed in a wide variety of different
configurations.
[0030] The disclosure herein describes improved cores to improve
the strength, fatigue life, and operational performance of the
coupler knuckle. Referring to FIGS. 1 and 2, a railroad coupler
knuckle is made from a mold 100 that includes cope and drag
sections 110, 150, respectively. The cope and drag sections each
include cavities 112, 152, respectively, into which a molten metal
or alloy is poured to cast the coupler knuckle. Disposed within the
drag section cavity 152 is a plurality of cores. This exemplary
embodiment includes a finger core 210, a pivot core 213, a kidney
core 212, and a pulling face core 211. As explained further below
and as shown in FIG. 3, once the cores are positioned within the
drag section cavity 152, the cope section 110 is lowered onto the
drag section 150, such that they also are at least partially
disposed within the cope section cavity 112, in order to begin the
process of forming the coupler knuckle. Note that in other
embodiments the cores may be disposed within the cope section
cavity such that the drag section is lowered onto the cope section
to begin the process of forming the coupler knuckle.
[0031] The finger core 210, pivot core 213, and kidney core 212 are
"internal" cores that help form interior cavities (i.e., the
finger, pivot and kidney cavities) of the coupler knuckle. The
pulling face core 211 is an "external" core that, along with the
outer surfaces 217, 219 of the mold cavities 112, 152,
respectively, forms the external surfaces of the coupler knuckle.
While three internal cores are identified, they may be configured
in a variety of ways. For example, the internal cores may be made
as three separate cores, such that three separate parts must be
joined to each other and then disposed within the mold prior to
commencing with the casting process. However, it often is desirable
to reduce the number of cores. An example of a casting made out of
a reduced number of cores is disclosed in U.S. Pat. No. 7,302,994
entitled "Method and System for Manufacturing a Coupler Knuckle."
The '994 provides that one or two internal cores may be used to
define the finger, pivot and kidney cavities. Such a reduction
results in less material being required overall to form the cores.
Moreover, reducing the number of cores also reduces the potential
for movement between the cores during the casting process, which
can result in some knuckle walls being thinner than others. This,
in turn, may reduce failures attributable to a non-uniformly cast
knuckle. In addition, reduction of the number of cores or reduction
in the overall size of a single core has been found to reduce
manufacturing costs.
[0032] For example, and as shown in FIG. 4 the pivot core 213 and
kidney core 212 have been combined into a fist core 215.
Accordingly, the fist core 215 may then be joined to a finger core
210, such that two as opposed to three parts need only be joined
prior to being disposed within a mold. In this exemplary
embodiment, the finger core 210 is about to be connected to the
fist core 215 through the interaction of an extension 214 on the
finger core 210 and an opening 216 on the pivot pin core 213.
[0033] The external pulling face core 211 includes a pulling face
mold portion 221 that allows for the development of the pulling
face portion 58 of the knuckle without any parting line running
through the pulling face. The external core repositions the parting
line at the pulling face from a center section 59 of the pulling
face portion, which is a high-stress area, to lower-stress areas,
which is about at least 2 inches in a vertical direction 64 (FIG.
6) above and below the center section 59, and can be closer to the
outer portions 60, 62 in a vertical direction 64 of the knuckle if
a full-height external core (i.e., an external core that is the
full height of the casting) is used.
[0034] Once cast, and as shown in FIGS. 5-6, the coupler knuckle 16
includes a tail section 20, a hub section 22 and a front face
section 24. The front face section 24 includes a nose section 52.
The pulling face portion 58, with center section 59, is disposed
inwardly from nose section. At least the center section 59 of the
pulling face portion 58 is substantially flat in a vertical
direction as defined by arrow 64 in FIG. 6.
[0035] As shown in FIG. 7, the pulling face portion 58 and in
particular the central section 59 of the coupler knuckle, acts to
bear against a similar surface 58' of a coupler knuckle 16' of an
adjacent railcar to couple the railcars together. Preferably the
central section 59 extends in the range of about 3.5 and 7 inches
in vertical direction 64 and about between 4.0 and 5.5 inches in
horizontal direction 65. Moreover, and as recognized by those
skilled in the art, the term "substantially flat" when used to
describe the central section 59 does not require a perfectly flat
surface. Rather, referring to FIG. 5B, inclined portions 57 of the
substantially flat surface are inclined at an acute angle .theta.,
which typically is in the range of about 0.5 to 1.5 degrees,
relative to a line extending in vertical direction 64 to facilitate
the removal of the coupler mold (cope or drag) from the
pattern.
[0036] Optionally, a central 53 of the nose section 52 may include
a cylindrical flag hole 54 opening, which may be formed by pins
positioned within the cope and drag sections 110, 150 of the
mold.
[0037] The hub section 22 includes a pivot pin hole 30 formed
therein for receiving a pivot pin to pivotally couple the knuckle
16 to a coupler for coupling to a railcar. The pivot pin hole 30 is
formed from at least a portion of the single internal core 10, 12.
The pivot pin hole 30 includes generally cylindrical sidewalls. The
tail section 20 of the knuckle 16 also includes a top pulling lug
46 and a bottom pulling lug 46a used to pull the knuckle 16 when
attached to the train (FIG. 5A).
[0038] A method for manufacturing the railcar coupler set forth in
the afore-identified embodiments is now described. Cope and drag
mold portions are provided, with each including internal walls,
formed of sand using a pattern or otherwise, that define at least
in part perimeter boundaries of a coupler knuckle mold cavity. As
noted above, the external core is utilized to form the pulling face
58 of the knuckle coupler. Together, the mold cavity and external
core correspond to the desired shape and configuration of the outer
surface of a coupler knuckle to be cast.
[0039] At least one internal core is positioned within either the
cope mold portion or the drag mold portion. As noted, there may be
one or more cores. For example, a single core may be configured to
define kidney, pivot pin, and finger core portions, such that only
one core need be disposed within the mold. Alternatively, there may
be a first internal core configured to define a kidney cavity and a
pivot pin cavity and a second core configured to define a finger
cavity, such that two cores must be joined and disposed within the
mold. By way of another example, and as has been described above,
the second core may be eliminated and instead the mold cavity can
be configured to include at a finger section that forms at least
one finger cavity of the coupler knuckle. The external core also is
positioned within either the drag or cope mold portion in order to
form the pulling face portion 58 of the coupler knuckle. Together,
the mold cavity and external core correspond to the desired shape
and configuration of the outer surface of a coupler knuckle to be
cast.
[0040] The cope and drag mold portions are closed with the internal
core(s) and external core there between. A molten metal or alloy is
then introduced, through known methods, which solidifies to form
the coupler knuckle. The presence of the one or more internal cores
and/or the finger section in the mold cavity will define the
kidney, pivot pin, and finger cavities of the coupler knuckle. The
presence of the external core will define the pulling face of the
coupler knuckle as described above.
[0041] Referring to FIG. 8, normally, when the cope and drag mold
portions 110, 150 are closed, a parting line or joint mark 300 is
formed between them, which will form on the exterior surface of the
coupler knuckle. However, and assuming in this embodiment that the
external core is to be placed within the drag portion cavity, the
presence of the external core will prevent the parting line joint
from forming on the central section of the pulling face portion and
instead cause it to form at the ends of the external core.
Preferably, the outer ends of the core will be at least 2 inches
out of range of the center section of the pulling face portion, and
more preferably will be located at the outer, lower stressed
portions of the knuckle and by the upper and lower portions 302,
304 of the external core (FIG. 2). Advantageously, this will
prevent the parting line joint from forming on the central section
59 of the pulling face portion 58. This is desirable because the
formation of parting line joints typically require the casting to
undergo a grinding process in order to remove them. Grinding can
affect the knuckle's surface finish and ultimately cause fatigue
failures and shorten the service life of the knuckle. Moreover, due
to the contact stresses the central portion of the pulling face
portion experiences when it engages with another knuckle, the
central portion is more susceptible to such failures. Exposing the
central portion to a grinding finish generally will increase the
change of such failures. Moreover, due to its location and its
arcuate geometry, the central section of the pulling face is very
difficult, and sometimes not even possible, to grind practically or
cost-effectively. Accordingly, moving the parting line away from
the central portion of the pulling face eliminates the need for
subjecting the central portion to such finishing operations.
[0042] Moreover, as contemplated by the presently-described
embodiments, at least a portion of the internal core and/or
external core is made from a high-density sand. Suitable sands
include chromite (iron magnesium chromium oxide (Fe, Mg)Cr.sub.2O))
or zircon (zirconium silicate (ZrSiO.sub.4)) and associated
derivatives. The use of a high-density sand such as chromite or
zircon, or respective chromite or zircon based derivatives, to form
at least a portion of a core provides an improved knuckle casting
surface finish because such sands have a finer particle size and a
lower thermal expansion rate than prior art sands of silica or
silica-based derivatives sands that typically are used to create
the mold and/or cores. Specifically, the use of a high-density sand
reduces problems associated with "shrinkage" or "micro-shrinkage."
Micro-shrinkage occurs when a molten metal that is introduced into
a mold during casting shrinks as it cools and solidifies. The
properties of the high-density sands used in the present
embodiments allow them to quickly diffuse heat and "chill" the
corresponding portion of the casting at a more rapid rate such that
shrinkage is minimized and sometimes even avoided. Beneficially,
this results in a casting having an improved surface finish and
reduces the likelihood of the formation of shrinkage defects in the
knuckle, which can include fins, ripples, scars, and even a void in
certain portions of the casting. Likewise, the lower thermal
expansion rate of high-density sands reduces the potential for the
core to contain buckles and cracks, thus reducing the potential
formation of veins on the casting. The presence of such
imperfections can cause the coupler knuckle to prematurely wear or
fatigue. Furthermore, the reduction of the presence of such
imperfections reduces the need for surface finish grinding, which
can subject the knuckle to further fatigue failures as described
above. Accordingly, and in particular, it is desirable to form the
pulling face mold portion of the external core from a high-density
sand in order to avoid the need for subjecting the pulling face
portion of the knuckle to casting. As described above, this surface
does not lend itself well to such finishing.
[0043] The use of high-density sands to form the internal and
external cores corresponding to the portion of the casting
containing the parting line joint may also reduce the need for the
casting to undergo parting line joint grinding, which, as described
above, has been shown to adversely affect the performance of the
coupler knuckle Notably, it is preferable to use a high-density
sand core that corresponds to the portion of the casting on which
the parting line joint forms in order to avoid the presence of
surface defects of the type described above. As described further
below, it also may be desirable to use a high-density sand core to
cast the pulling face portion of the front face section.
[0044] Accordingly, such high-density sands are beneficial over
silica sands or silica sand derivatives, which typically are used
to cast the knuckle and as is briefly described in U.S. Pat. No.
7,337,826 entitled "Railway Car Coupler Knuckle Having Improved
Bearing Surface." As described below, high-density sands provide an
increased chilling effect and undergo less thermal expansion during
casting, and have a finer particle size than silica sands. In turn,
such benefits result in the coupler knuckle having better
dimensional stability, better solidity, and a superior surface
finish, which reduces the potential for fatigue failures.
[0045] Moreover, the use of a high-density sand can replace the
need for the inclusion of risers in the mold in this area to "feed"
the volumes of the casting that are prone to shrinkage with
additional casting material. Once a casting is complete, however,
any excess material must be removed by surface grinding. The
presence of risers and/or ingates also limits the ability to cast a
knuckle having a precise profile and/or contour at its connection
point. Such disadvantages subject the casting to fatigue failures
as described above.
[0046] Moreover, in addition to the reasons described above, it is
not practical to include risers on some areas of the casting. The
pulling-face portion is one such area. The arcuate shape of the
pulling face portion in the horizontal direction, as well as its
susceptibility to stress failures as described above, the pulling
face portion does not lend itself well to surface grinding.
Moreover, as described above it is desirable for the pulling face
portion to have a substantially flat surface. The inclusion of
risers does not promote the formation of such a flat surface
without subjecting the surface to further grinding, which again
exposes the pulling-face portion to the afore-described
disadvantages.
[0047] Likewise the use of high-density sands reduces the need for
chills, which are used to absorb and removed heat during casting.
Chills may be "external" to the casting or "internal" to the
casting, with internal chills ultimately becoming part of the
casting. Accordingly, because internal chills become part of the
casting, care must be taken in choosing the proper chill material
so that it is compatible with the casting material. Otherwise, the
chill's fusion to the casting will be improper or incomplete, which
may cause premature failure of the casting or require the casting
to undergo further finishing and/or repairs. If external chills are
not carefully placed, they may leave scars or other defects on the
casting's surface that requires the casting to undergo extra
finishing operations such as grinding, which may adversely affect
the knuckle's surface finish. Moreover, because external chills
typically are formed as small pieces of metal, they often have to
be attached to an external core, which as noted above is made of
silica which does not provide the benefits of high-density sand
cores, so that they do not fall out of place. These must also be
carefully placed so that the casting receives the benefit of the
targeted area of the chill. As to both external and internal
chills, they are effective only as to smaller surface areas and
tend to lose their effectiveness at volumes of the knuckle further
away from the chill. The use of the high-density sand core,
particularly the external core, eliminates these problems because
the core can be formed to be the height of the knuckle and cover
any desired surface area and still not lose its effectiveness.
Notably, the use of high-density sand external core(s) also
eliminates the potential for surface imperfections such as those
described above, eliminates problems associated with incorrectly
placed chills, and the general expense associated with chills,
especially internal chills because they must be made of a material
compatible with the casting.
[0048] In fact, in other embodiments the external core may be made
of other materials that provide the benefits discussed above. In
one preferred embodiment, the external core, which functions as a
"chill core," may be made from graphite. Graphite is desirable
because it provides for higher cooling rates due to having high
levels of thermal conductivity. Using a graphite chill core also
provides the benefits discussed above as to avoiding
micro-shrinkage and the use of external chills such that further
surface grinding in the central section 59 upon formation of the
casting may be avoided. Moreover, a graphite chill core also avoids
the problems related to the requirement of careful placement of
external chills as discussed above. In other embodiments, the chill
core may be metallic, and preferably can be made from cast gray
iron. It is desirable to select a grade of cast iron that has a
larger proportion of graphite flakes since the thermal conductivity
of gray iron is primarily a function of the graphite flake content.
The higher the graphite flake count the higher the probability that
the flakes will be touching each other, which gives gray iron a
high conductivity. Another suitable example of a metallic chill
core is one made from cast steel. Moreover, in other embodiments
the chill core may be made from silicon carbide, which is desirable
in applications involving less severe chilling requirements.
Notably, the term "chill core" also may be applied to external
cores that include at least portions made from zircon, chromite,
their respective derivatives, as well as other high-density sands
given their function of reducing micro-shrinkage. Such high-density
sands are desirable because, in addition to the benefits described
above, they are more readily available at foundries and are less
expensive.
[0049] The terms and descriptions used herein are set forth by way
of illustration only and are not meant as limitations. Those
skilled in the art will recognize that many variations can be made
to the details of the above-described embodiments without departing
from the underlying principles of the disclosed embodiments. For
example, and referring to FIG. 9, although a coupler knuckle has
been described, the above methods and systems may be used when
created the coupler itself. The coupler 18 couples or connects the
knuckle 16 to a railway freight car (not shown).
[0050] Furthermore, although the above-described techniques and
cores have been described for use with respect to the formation of
the pulling face portion, they may be used to form any portion of
the knuckle (or coupler body) casting. Moreover, in one embodiment,
simulation software may be used to determine where the knuckle (or
coupler body) is prone to experiencing surface finishing failures
and stress in order to predetermine where it may be desirable to
use a high-density sand core. The simulation of such failures also
may help to determine where it may be desirable to locate such
cores in order to move the parting line joint that forms on the
casting. Likewise, the software may be used to predict the
formation of hot spots, which again may help determine where it is
desirable to use a high-density sand core. An example of suitable
software is provided by Magma Foundry Technologies in Schaumburg,
Ill.
[0051] Moreover, the steps of the method disclosed herein need not
be executed in a certain order, unless specified, although they may
have been presented in that order in the disclosure. By way of
further example, the configuration of the cores described herein
should not be limited to those described, as one skilled in the art
would recognize such cores may be configured in various ways to
produce the disclosed embodiments. Therefore, is to be understood
that it is the following claims, including all equivalents, which
are intended to define the spirit and scope of this invention.
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